1. Field of the Invention
The present invention relates to a synchronizing apparatus for use with an editing apparatus that edits a video signal and an audio signal or the like, for example.
2. Description of the Prior Art
U.S. Pat. No. 4,428,001 describes a conventional editing apparatus that edits a video signal. The conventional editing apparatus that edits a video signal and an audio signal uses a synchronizing apparatus for synchronizing a video signal and an audio signal.
A synchronizing method of synchronizing a video signal and an audio signal by this conventional synchronizing apparatus will be described below in which case a video signal is an NTSC video signal and a sampling frequency of an audio signal is 44.1 kHz.
A field frequency of the NTSC video signal becomes 315/22 MHz (=14.31818 MHz).div.910.div.262.5=60.times.1000/1001 Hz, i.e., 59.94005994 Hz.
The number of samples of digital audio signal per field becomes 44100 Hz/(60.times.1000/1001 Hz), i.e., 735.735. As will be understood from this value, the number of samples of the digital audio signal per field is 735.735 and contains a fraction of 0.735 so that the digital audio signal cannot be synchronized with the video signal at every field.
To solve this problem, it is proposed that the digital audio signal is synchronized with the video signal at every 200 fields in which the number of samples of the digital audio signal coincides with a vertical synchronizing signal. According to this well-known method, a gain of a sync. generator is locked in synchronism with a reader sequence. The number of samples of digital audio signals at 200 fields is 44.1.times.10.sup.3 (315/22.times.10.sup.6 .div.910.div.525.div.100), i.e., 147147. According to the prior art, by utilizing the above technique, the number of samples per field is counted by a counter and this count operation is concluded in 200 fields at the unit of 4 fields.
A pattern that 147147 samples of 200 fields are counted by the counter becomes (735+735.times.3)+(735+736.times.3).times.49. Audio samples are allocated to the fields as follows. Field Nos. are assigned to the fields and digital audio data is counted by a count number predetermined in response to the field No. when a video signal is reproduced. Then, digital audio data corresponding to the count number is allocated to the field of the corresponding video signal.
FIG. 1 of the accompanying drawings is a schematic diagram used to explain an example of a conventional synchronizing apparatus. In FIG. 1, reference numerals f1 to f200 depict 1st field to 200th field and g1 to g200 depict fractions (shift amounts) of the number of samples of digital audio at the fields, respectively. In FIG. 1, reference numeral s1 designates a vertical synchronizing position.
As shown in FIG. 1, the shift amount g1 at the 1st field f1 relative to the vertical synchronizing position s1 becomes 0.735 and the count number becomes 735; the shift amount g2 at the 2nd field f2 relative to the vertical synchronizing position s1 becomes 1.47 and the count number becomes 735; the shift amount g3 at the 3rd field f3 relative to the vertical synchronizing position s1 becomes 2.205 and the count number becomes 735; the shift amount g4 at the 4th field f4 relative to the vertical synchronizing position s1 becomes 2.94 and the count number becomes 735; and the shift amount g5 at the 5th field f5 relative to the vertical synchronizing position s1 becomes 3.675 and the count number becomes 735. The shift amount g5 at the 5th field f5 becomes maximum.
The shift amount g6 at the 6th field f6 relative to the vertical synchronizing position s1 becomes 3.41 that is smaller than the shift amount g5 at the 5th field f5 by 0.265 and the count number becomes 736; the shift amount g7 at the 7th field f7 relative to the vertical-synchronizing position s1 becomes 3.145 that is smaller than the shift amount g6 at the 6th field by 0.265 and the count number becomes 736; the shift amount g8 at the 8th field f8 relative to the vertical synchronizing position s1 becomes 2.88 that is smaller than the shift amount g7 at the 7th field by 0.265 and the count number becomes 736; the shift amount g9 at the 9th field f9 relative to the vertical synchronizing position s1 becomes 3.615 that is larger than the shift amount g8 at the 8th field f8 by 0.735 and the count number becomes 735; the shift amount g10 at the 10th field f10 relative to the vertical synchronizing position s1 becomes 3.35 that is smaller than the shift amount g9 at the 9th field f9 by 0.265 and the count number becomes 736; the shift amount g11 at the 11th field f11 relative to the vertical synchronizing position s1 becomes 3.085 that is smaller than the shift amount g10 at the 10th field f10 by 0.265 and the count number becomes 736; the shift amount g12 at the 12th field f12 relative to the vertical synchronizing position s1 becomes 2.82 that is smaller than the shift amount g11 at the 11th field f11 by 0.265 and the count number becomes 736; . . . ; the shift amount g196 at the 196th field f196 relative to the vertical synchronizing position s1 becomes 0.06 and the count number becomes 736; the shift amount g197 at the 197th field f197 relative to the vertical synchronizing position s1 becomes 0.795 that is larger than the shift amount g196 at the 196th field f196 by 0.735 and the count number becomes 735; the shift amount g198 at the 198th field f198 relative to the vertical synchronizing position s1 becomes 0.53 that is smaller than the shift amount g197 at the 197th field f197 by 0.265 and the count number becomes 736; the shift amount g199 at the 199th field f199 relative to the vertical synchronizing position s1 becomes 0.265 that is smaller than the shift amount g198 at the 198th field f198 by 0.265 and the count number becomes 736; and the shift amount g200 at the 200th field f200 becomes 0 that is smaller than the shift amount g199 at the 199th field f199 by 0.265 and the count number becomes 736. Thus, the processing is ended. That is, the digital audio signal is synchronized with the video signal by resetting the counter at the 200th field f200.
When the number of samples of digital audio data is calculated as (735+735.times.3)+(735+736.times.3).times.49=147147 as described above, the shift amount g5 (3.675) of five times in four times and one time of 735 samples becomes maximum. Subsequently, as shown by arrows h1 and h2 of FIG. 1, each sample is shifted 0.06 from the shift amount g4 (2.94) at the 4th field f4 at the unit of (735+736.times.3) and returned to the original sample by 0.06.times.49, i.e., 2.94 samples.
As shown in FIG. 1, the shift amount g4 at the 4th field f4 is 2.94 and the shift amount g8 at the last 8th field f8 of the 5th field f5 to the 8th field f8 is 2.88, i.e., there is a shift amount of 0.06. Similarly, the shift amount g8 at the 8th field f8 and the shift amount g12 at the 12th field f12 of the 9th field f9 to the 12th field f12 is 2.82, i.e., there is a shift amount of 0.06.
Similarly, the shift amount g196 at the 196th field f196 is 0.06 and the shift amount g200 at the last 200th field f200 of the 197th field f197 to the 200th field f200 is 0, i.e., there is a shift amount of 0.06.
When the audio signal and the video signal are edited in actual practice, a vertical synchronizing (sync.) signal is generated on the basis of a reference video signal, for example. Then, after the counter is reset by this vertical sync. signal, the counter starts the counting and the audio signal and the video signal are synchronized by the pattern of (735+735.times.3)+(735+736.times.3).times.49 at every 200 fields.
Since however the generator-lock circuit is effected in synchronism with the sequence of a reader in actual practice, the field number read by the reader and the field number generated by the sync. generator are shifted from each other by one sample. Therefore, upon editing, a pre-roll time of 200 fields is required in addition to a time during which a tape speed is fine adjusted to match the tape positions.
The pre-roll time of 200 fields becomes 1/60.times.1001/1000.times.200, i.e., 3.336666666 seconds. In this case, 1001/1000 represents a ratio of a color frequency 15.73 kHz and a black and white frequency 15.75 kHz.
There is then the disadvantage that the conventional synchronizing apparatus requires the pre-roll time of 200 fields, i.e., 3.336666666 in addition to the time during which the tape speed is fine adjusted to match the tape positions.